1. Field of the Invention
The present invention relates to a hybrid ink jet printer for printing by discharging ink to a print medium such as a continuous paper by means of an ink jet head, and a method of hybrid ink jet printing, specifically; to a hybrid ink jet printer configured capable of discharging different kinds of inks by a plurality of printing units, and a method of printing in the hybrid ink jet printer so configured.
2. Description of the Related Art
In conventional publicly known offset printing, printing can be performed not only using ordinary ink (for exampling, newspaper ink), but also using ultraviolet curable ink.
This ultraviolet curable ink instantaneously cures and dries when irradiated with ultraviolet light. In addition, the ultraviolet curable ink displays strong film strength from immediately after transfer, hence does not require a waiting time until post-processing. Therefore, a printer that prints using ultraviolet curable ink can print also on print media such as coated paper that has undergone surface processing and is difficult for the ink to penetrate, films, or the like. That is, if printing is performed using ultraviolet curable ink, printing can be performed on a wide variety of print media.
Meanwhile, an ink jet printer is proposed as a different method of printing to an offset rotary press (refer to Patent Document 1 listed below). Two kinds of printing systems of the ink jet printer exist, namely a single-pass system that, when a print medium passes below four colors' worth of inkjet heads (an inkjet head group) aligned in a print medium running direction and each having a length capable of single color printing of an entire paper width, prints all of the colors concurrently, and a multi-pass system that, while an ink jet head travels back and forth multiple times in a paper width direction over a print medium, sprays ink onto the print medium. The single-pass system has a feature that increased printing speed can be realized, while the multi-pass system has a feature that precise printing can be realized.
Incidentally, in order to configure a printer capable of handling a wide variety of print media, ultraviolet curable ink should be employed as mentioned above, but ultraviolet curable ink suffered the problem of being expensive compared to ordinary ink and of incurring high running costs. Therefore, it was desired that, when the print medium could sufficiently handle ordinary ink, printing could be performed by cheap price ordinary ink, and that, when good printing could not be realized by ordinary ink as in the case of coating paper, printing could be performed by ultraviolet curable ink.
Accordingly, as shown in FIG. 6, a method was proposed that installs a total of two off set rotary presses, that is, one each of, respectively, an offset rotary press 70 that prints using ordinary ink and an offset rotary press 80 that prints using ultraviolet curable ink, and thereby selectively uses the inks to enable handling of a wide variety of print media. If two offset rotary presses 70 and 80 are installed in this way, when a paper roll is set in the print paper feed unit, selection can be made of the offset rotary press 70 that prints using ordinary ink or the offset rotary press 80 that prints using ultraviolet curable ink, thus enabling handling of a wide variety of print media. However, a method where two offset rotary presses are installed requires securing of a large installation space, and therefore cannot be realized, in a place having no space. Accordingly, a printer was desired that was capable of handling a wide variety of print media while still being compact.
In contrast, a method of printing is proposed that suppresses running costs by switching the inks used. That is, a method of printing was proposed in which, when printing on a print medium where good printing can be realized by ordinary ink, ordinary ink is set as the ink supplied, and when printing on a print medium where good printing cannot be realized by ordinary ink, ultraviolet curable ink is set as the ink supplied.
However, the method of printing that switches the ink supplied from an ink supply device to match the print medium had the problem that trouble occurs in a group of ink transfer rollers, or a plate cylinder and blanket, and so on, that are traversed when transferring the ink. As shown in FIG. 7, printing by an offset rotary press is performed by ultraviolet curable ink being supplied from an ink fountain 91, the supplied ultraviolet curable ink traversing a group of ink transfer rollers 92 to be shifted to a plate cylinder 93, and further to be shifted from the plate cylinder 93 to a blanket cylinder 94, after which the ultraviolet curable ink is transferred from the blanket cylinder 94 to continuous paper. That is, the ultraviolet curable ink passes the same route as the route along which ordinary ink moves, hence traverses the same group of ink transfer rollers 92, plate cylinder 93, and blanket cylinder 94 as the group of ink transfer rollers 92, plate cylinder 93, and blanket cylinder 94 that are traversed by ordinary ink when ordinary ink is employed.
The group of ink transfer rollers 92, or a plate (not illustrated) on the plate cylinder 93 and a blanket (not illustrated) on the blanket cylinder 94, and so on, although never causing trouble simply when constituents of ordinary ink adhere, do cause trouble when ultraviolet curable ink adheres. Specifically, low molecular constituents of high polarity included in ultraviolet curable ink cause swelling of the group of ink transfer rollers 92 and rubber of the blanket on the blanket cylinder 94 for use in ordinary newspaper printing, and also dissolve resin forming a picture line part of the plate on the plate cylinder 93 for use in ordinary newspaper printing.
In order to prevent these troubles, an ultraviolet curable ink is proposed (for example, Daicure Hy-Bryte) that has high lipophilicity of the ink and has aptitude for the plate cylinder, group of ink transfer rollers and blanket of a printer for use in ordinary newspaper printing. The provision of such an ultraviolet curable ink has made it possible to realize selective use of inks simply by switching the ink supplied from the ink fountain without performing large maintenance work such as replacement of the group of ink transfer rollers 92 or replacement of the plate on the plate cylinder 93, and so on ( refer to Patent Document 2 listed below).
[Patent Document 1] JP 2009-226863 A
[Patent Document 2] JP 2004-351757 A